Vol. VI] WEAVER— OLIGOCENE OF KITSAP CO., WASH. 43 



Seattle or middle, and the Twin River or upper. The lower 

 and middle divisions are stated to occur at Restoration Point. 

 The San Lorenzo formation is described as the "sandstones 

 overlying the lower Astoria basalts west of Port Orchard 

 Sound and forming the lower half of the Bainbridge Island 

 section of the Seattle monocline." The Seattle formation is 

 said to consist "of the upper beds of the northward dipping 

 Seattle monocline extending from Restoration Point on Bain- 

 bridge Island across Admiralty Inlet." The Twin River for- 

 mation is not believed to occur in the Puget Sound basin. 



In none of the investigations so far undertaken has an at- 

 tempt been made to work out the details of the stratigraphy. 



GENERAL STATEMENT CONCERNING THE MA- 

 RINE TERTIARY IN WESTERN WASHINGTON* 



All of the pre-glacial areal outcrops in the western part 

 of the state with the exception of the central and western por- 

 tions of the Olympic Peninsula and the San Juan Islands are 

 of Tertiary age. Both sedimentary and igneous rocks are 

 present. They were formed during the Eocene, Oligocene and 

 Miocene epochs. With the exception of possible marine sedi- 

 ments in the extreme western portion of Chehalis County, no 

 rocks of definite Pliocene age are known to exist. The history 

 of the Pliocene in western Washington must be sought in terms 

 of diastrophism and erosion. 



During the Eocene epoch there were formed deposits of 

 marine, brackish and freshwater origin. Intercalated with 

 these are lavas and tuff of andesitic character. These deposits 

 attain a total maximum aggregate thickness of at least 10,000 

 feet. The marine invertebrate faunas occurring within these 

 strata indicate that only the Tejon or upper Eocene is present 

 in western Washington. 



Five distinct marine faunal zones can be recognized in the 

 post-Eocene formations of western Washington: 



Yoldia strigata zone Upper Miocene 



Area montereyana zone Lower Miocene 



*A detailed report on the "Tertiary Formations of Western Washington" by the 

 writer will be issued as a bulletin of the publications of the Washington State Geo- 

 logical Survey. Accompanying this report are detailed areal and structural geological 

 maps of the western portion of the state. 



